1. Field of the Invention
The present invention relates to a case for an electronic device an a production method of the case, and particularly to an electronic device case made by using magnesium or a magnesium alloy and a production method thereof.
2. Description of the Prior Art
A metal material or an alloy material having an excellent mechanical characteristic and showing an excellent touch feeling is widely used for an external casing material in various fields. Especially, a magnesium alloy material is the lightest material among practical materials, showing an excellent cutting property, a high strength/density ratio as well as an excellent die casting property, and its application for a casing has been examined in various fields such as computers, audio apparatuses, communication apparatuses, electronic apparatuses, and the like.
However, the magnesium alloy has an inferior resistance for corrosion and is easily oxidized in the atmosphere, forming a thin film on the surface, which deteriorates the external view. Especially when subjected to a precision cutting, corrosion resistance becomes a big problem.
For this, in order to improve the corrosion resistance and abrasion resistance of the magnesium alloy material, conventionally, anodizing and chemical conversion treatment has been carried out by using a heavy metal salt such as chromate (VI), manganate, permanganate or the like, and fluoride.
However, there arises a problem that the metal feeling is deteriorated where the anodizing or the chemical conversion treatment is carried out.
Use of heavy metal salts in anodizing or the chemical conversion treatment also brings about a problem of contamination of the environment.
There is also a finishing method of a magnesium alloy material by carrying out a shot blast to obtain a rough surface and then painting the rough surface. In this case, the metal feeling is completely lost.
As has been described above, use of a magnesium alloy material for a casing of an electronic apparatus has not been implemented in practice because of the aforementioned problems.